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In Italy, Electric Buses Wirelessly Pick Up Their Power

By Paul Stenquist May 30, 2012 2:50 pmMay 30, 2012 2:50 pm

Conductix-WampflerPosition markings for a wireless charging system with coils integrated in the road surface in Turin.

Battery-powered buses that do not require frequent stops at charging depots might seem a maybe-someday proposition. But Conductix-Wampfler, a wireless-charging engineering company based in Weil am Rhein, Germany, claims the bus of the future is fully operational on the streets of Turin and Genoa, Italy, and has been for 10 years.

The Conductix-Wampfler IPT Charge system, which powers about 30 buses in the northern Italian cities, relies on primary coil charging units in the road surface at bus stops, terminals and hubs. The secondary coil, which receives the charge, is in the bus chassis. When a bus stops at a charging station, the coils are positioned within 40 millimeters, or roughly 1½ inches, of each other.

Batteries are fully charged overnight at the depot and topped off at each charging point on the route, ensuring sufficient range for reaching the next charging station. The topping-off charge refreshes about 10 to 15 percent of the battery’s capacity and, according to Conductix-Wampfler, can be done while passengers board and exit. Buses serving Turin travel about 200 kilometers, or roughly 125 miles, a day without requiring a stop for a prolonged period or a return to the depot for charging, the company claimed.

Conductix-WampflerSystem layout of a bus equipped with inductive charging capability.

Electric municipal buses, of course, are nothing new. In the 1950s they circulated through many urban cores in the United States. The electricity, however, was delivered by overhead wires carrying power directly from the grid to pivoting relay points on the buses’ roofs. Though some holdouts remain, these fragile and unsightly systems have largely given way to buses powered by internal-combustion engines.

Conductix-Wampfler claims its energy transfer system, called inductive power transfer, successfully sends 95 percent of the charge to the secondary coil. The 5 percent transfer loss is negligible.

The magic at work here is magnetic resonance coupling, a principle also used by manufacturers of charge pads, or mats, for mobile devices. But even though companies like WiTricity, Evatran and HaloIPT are at work on wireless charging for electric vehicles, automotive applications of the technology, let alone for 10 years in the field, are few.

While the cost of electric buses exceeds that of conventionally powered vehicles, Conductix-Wampfler estimates a payback period of less than four years, based on an electric power cost of $9,000 a year versus a diesel fuel cost of $50,000. The company is working with Daimler to develop a plugless charging system for passenger cars. It also says it plans pilot and test projects of its technology in American cities, including Los Angeles and Chattanooga, Tenn.

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